fix(@angular-devkit/schematics): handle zero or negative length removals in update buffer

This came up while fixing an issue in a Framework migration (https://github.com/angular/angular/pull/43776/files#diff-365738677fa9dfb9fb2c4fac7c75addb58e5a35182603e722e736cc3f24bbf5bR55). The `UpdateBuffer` stops recording changes if a removal with a zero length occurs. This doesn't appear to be an issue with `UpdateBuffer2`, but considering that the former is still being used and that the fix is trivial, I decided to proceed with it.

I've also aligned the behavior between `UpdateBuffer` and `UpdateBuffer2` when dealing with negative removals.

Author: crisbeto

packages/angular_devkit/schematics/src/utility/update-buffer.ts

@@ -238,8 +238,15 @@ export class UpdateBuffer extends UpdateBufferBase {
   }
 
   protected _slice(start: number): [Chunk, Chunk] {
-    // If start is longer than the content, use start, otherwise determine exact position in string.
-    const index = start >= this._originalContent.length ? start : this._getTextPosition(start);
+    let index: number;
+
+    if (start >= this._originalContent.length) {
+      index = start;
+    } else if (start < 0) {
+      index = this._originalContent.length + start;
+    } else {
+      index = this._getTextPosition(start);
+    }
 
     this._assertIndex(index);
 
@@ -294,8 +301,11 @@ export class UpdateBuffer extends UpdateBufferBase {
   }
 
   remove(index: number, length: number) {
-    const end = index + length;
+    if (length === 0) {
+      return;
+    }
 
+    const end = index + length;
     const first = this._slice(index)[1];
     const last = this._slice(end)[1];
 

packages/angular_devkit/schematics/src/utility/update-buffer_spec.ts

@@ -178,6 +178,26 @@ describe('UpdateBuffer', () => {
       buffer.remove(0, 6);
       expect(buffer.toString()).toBe('ABC');
     });
+
+    it('is able to insert after a zero-length removal', () => {
+      const mb = new UpdateBuffer(Buffer.from('123'));
+
+      mb.remove(0, 0);
+      expect(mb.toString()).toBe('123');
+
+      mb.insertRight(0, Buffer.from('0'));
+      expect(mb.toString()).toBe('0123');
+    });
+
+    it('is able to insert after a negative-length removal', () => {
+      const mb = new UpdateBuffer(Buffer.from('123'));
+
+      mb.remove(0, -1);
+      expect(mb.toString()).toBe('3');
+
+      mb.insertRight(0, Buffer.from('0'));
+      expect(mb.toString()).toBe('03');
+    });
   });
 
   describe('generate', () => {
@@ -355,6 +375,26 @@ describe('UpdateBuffer2', () => {
       buffer.remove(0, 6);
       expect(buffer.toString()).toBe('ABCDEF');
     });
+
+    it('is able to insert after a zero-length removal', () => {
+      const mb = new UpdateBuffer2(Buffer.from('123'));
+
+      mb.remove(0, 0);
+      expect(mb.toString()).toBe('123');
+
+      mb.insertRight(0, Buffer.from('0'));
+      expect(mb.toString()).toBe('0123');
+    });
+
+    it('is able to insert after a negative-length removal', () => {
+      const mb = new UpdateBuffer2(Buffer.from('123'));
+
+      mb.remove(0, -1);
+      expect(mb.toString()).toBe('3');
+
+      mb.insertRight(0, Buffer.from('0'));
+      expect(mb.toString()).toBe('03');
+    });
   });
 
   describe('generate', () => {